1. Field of the Invention
The present disclosure relates generally to bone treatment devices, and more particularly to a bone screw used to treat a bone fracture wherein the bone screw is suitable for treating fractures of the femur including trochanteric, intertrochanteric and femoral neck fractures.
2. Description of Related Art
Orthopedic fixation systems used for stabilizing a fracture often include an internal fixation device, typically an elongated implant such as a nail, screw or pin, inserted into the intramedullary canal of the bone to stabilize the fracture and promote healing. Such fixation systems are suitable for use in treating fractures of the neck, head, intertrochanter, subtrochanteric, pathologic and certain ipsilateral shaft and neck fractures of the femur. The femur generally includes an elongated shaft, a ball shaped head that fits into the hip socket and a neck connecting the ball to the shaft. The shaft also includes a greater trochanter and a lesser trochanter.
For example, if the neck of the femur sustains a fracture a bone nail is inserted into the intramedullary canal and a bone screw inserted through an aperture in the head of the nail. The bone screw spans the fracture and threadably engages the femoral head. Typically, a smooth bore forms the aperture in the end of the nail. The bone screw extends through the smooth bore and rotates as it threadably engages the femoral head. Once the bone screw is suitably tightened, it is left in place during the healing process. In some instances, for example when the patient puts weight on the hip, the fracture will compress or settle. Thus, bone screw migration is one problem that may occur during the healing process. Specifically, when the patient puts weight on the hip the femoral head may move with respect to the femur; that is, the femoral head may slide medially or laterally at the fracture. The movement may be due to weakness in the bone, bone deterioration, misalignment of the fracture or other factors.
Depending upon the type of connection or engagement between the bone screw and the bone nail, movement of the femoral head with respect to the femur may result in “cut-out,” that is the externally threaded end of the bone screw cuts or extends through the femoral head. Cut-out may occur when the bone screw is fixedly secured to the bone nail and does not move in the aperture. As the femoral head moves, due to settlement of the fracture or bone deterioration, it slides or travels along the bone screw. Eventually the femoral head moves close enough to the femur that the threaded end of the bone screw breaks through or pierces the femoral head and extends into the hip joint.
If the bone screw is slidably fixed in the aperture, that is the bone screw is constrained against rotation but is allowed to slide longitudinally in the smooth bore of the aperture, compression of the fracture may cause the head of the bone screw to extend outward significantly past the outer surface of the femur creating a raised surface that can cause pain at the hip joint. In addition, leaving the bone screw free to move with respect to the bone nail may cause the bone screw to migrate or loosen, thus creating a risk of failure at the fracture.
The features and advantages of the disclosure will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by the practice of the disclosure without undue experimentation. The features and advantages of the disclosure may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.